The present invention generally relates to a data processing unit for converting waveform information or data of image data (e.g. drawings, documents, pictures, color pictures, medical images and so on) and other data to a data form capable of being processed on a computer and/or performing recognition of image data, reduction of noise, analysis of data and/or other processing to thereby allow these data to be processed by the computer. More particularly, the present invention is concerned with a method of filtering a large amount of data such as document data, image data, drawing data or the like used in OA, FA and other equipment.
According to the filtering techniques employed heretofore, an (n.times.m) size image or picture is cut out around a point or location to be processed by a filter having a size, for example, of (n.times.m). Another method involves dividing the (n.times.m) size filter into sub-filters having a size on the order of (3.times.3), wherein filtering is performed (2.times.2).times.(m-2) times. In either method mentioned above, the number of times the processing is executed for a whole image depends largely on the filter size values n and m. This sort of filtering procedure is discussed in Makoto Nagao "Digital Image Processing", Kindai Kagakusha Inc. of Japan, (1978), pp. 376-379.
The above-mentioned prior art filtering techniques intrinsically suffer from the problems mentioned below. In the filtering processing frequently required in the processing of drawings, documents, pictures or other images in offices, the filter size is in the range of 10.times.10 to 50.times.50. To meet this requirement, filtering with the filter size of (3.times.3) must be repeated 8.times.8 (=64) to 48.times.48 (=2304) times, which is practically impossible in many applications. To deal with this problem, a method is known by which the above is carried out by resorting to the use of a dedicated device. According to this method, some images such as TV images can be processed by using a filter of a size in the range of (3.times.3) to (5.times.5) and, if necessary, by repeating filtering only a small number of times. However, in the field of OA equipment and others, there exists a need for a filter of a greater size as well as a dedicated device for attaining a high speed operation, which of course implies significant increase in expenditures. Under the circumstances, difficulty is encountered in implementing such image processing system in commercially acceptable products.
It must further be pointed out that the prior art image processing method relies on the arithmetic operation on a pixel-by-pixel basis. To this end, an image data buffer of extremely large capacity is required for storing the image data of the amount corresponding to the number of pixels (picture elements) to be processed. Furthermore, at the present state of the art of facsimile and optical disc systems, storage of data in the form of compressed code is prevalent. In this connection scheme, according to the prior art method, the compressed code has to be developed once to the image data before being processed, thus presenting a problem that the merits of recording in the form of compressed data (i.e. reduction in the data amount) can not be taken advantage of. Additionally, because of a large amount of drawing and document data to be handled by the systems installed in offices, workshops and hospitals, the data are ordinarily stored in magnetic discs, floppy discs, optical discs and others. In such case, a great deal of time is required in the data transfer due to the necessity of accessing a great number of times the image data stored in these storage devices.